Recently, a digital content has been easily enjoyable on a home network which is built out in the home, according to development in an electronic technology and a communication technology. The digital content is capable of providing a beautiful image with a high definition, with respect to a user, and is capable of providing various associated information services. On the other hand, an image quality of the digital content is not degraded in the case of being copied by a digital process, unlike copy of analog data. For this reason, it is a problem that copyright protection is performed in order to prevent illegal copy.
Thus, there is digital transmission content protection (DTCP), as a standard set to prevent the illegal copy, from the viewpoint of the copyright protection. The DTCP is a copyright protection method which is used for preventing copy of a sound or an image in a home network/a personal network, and is mainly used together with a digital living network alliance (DLNA) which is an interconnection guideline for sharing image or sound data between digital devices. In the DTCP, a common key encryption method is used in which common keys are exchanged between the digital devices, and thus, encryption is performed. A technology of transmitting and receiving the digital data between the digital devices, by the common key, for example, is disclosed in Patent Document 1.
On the other hand, a cooperation function between a smart phone and a home electrical appliance, such as controlling the home electrical appliance by the smart phone, or distributing the digital content, has attracted attention, according to high functionality of the smart phone. As a technology relevant to the content transmission, a technology is disclosed in Patent Document 2, in which a user selects an external output device (a TV or the like) by a smart phone (a mobile phone unit), and process ability of the selected external output device and identification information of identifying the output device are specified. Then, a request is performed with respect to a home server such that a content suitable for the process ability of the external output device is transmitted to the external output device, and thus, the content transmitted from the home server is received by the external output device, and is output as an image.